The present invention relates generally to probing systems and more particularly to a probe head holder for a measurement probe that is attachable to a probing arm of a probing system.
Hand held measurement probes are used to acquire electrical signals from component leads and test points of a device under test and couple these signals to a measurement instrument, such as an oscilloscope, logic analyzer and the like. These probes are also used in conjunction with probing stations to acquire signals from integrated circuit wafers and packages, surface mounted components and test points. The probing station has a probe arm on which is rotatably attached a probe head holder. The probe head holder includes a probe head mount and associated attachment hardware to secure the probe head to the probe head mount. The probe head of the measurement.probe is attached to the holder and the arm is positioned over the device under test such that the probe tip or tips of the measurement probe are positioned on the electrical contact of the device being tested. The positioning of the probe arm and the placement of the probe on the device under test is most often performed by a user using a magnifying device.
There are a number of different ways that a probe head is attached to the probe head holder. The probe head holder of the EZ Probe Arm, manufactured and sold by Cascade Microtech, Beaverton, Oreg., has a grooved-block probe head mount and screw down clamps. The probe head is positioned in the groove and the metal clamps are positioned across the probe head and screwed into the mount. The EZ Probe arm includes a joy stick in a base that positions the probe on the device under test. The probe head holder for the PPM203B Articulated Arm, sold by Tektronix, Inc., Beaverton, Oreg., has a probe head holder with a slotted hole that receives the probe head. One side of the slot has a threaded aperture that receives a screw that is inserted through a second aperture formed in the other side of the slot. The probe head is secured in the probe head mount hole by tightening the screw in the slot. Probe head holders having different holes sizes and shapes may be attached to the articulated arm to accept different sized and shaped probe heads.
Users have adapted the existing probe head holders by using binder clips, such as manufactured by Acco USA, Inc., Wheeling Ill., to secure the probe heads to the probe head mounts without using the attachment devices of the holders. This adaption allows the probe head to be quickly and securely attached to the probe head mount. User have also used zip ties to secure the probe head to existing probe head holders. A drawback to using zip ties is that the ties have to be cut to free the probe from the holder. It is also possible to use rubber bands to secure probe heads to probe head mounts but, because of the low hoop strength of rubber bands, it would require a large number of rubber bands to adequately secure a probe head to a probe head mount. Looping a large rubber band multiple times around a probe head and probe head mount is also possible but the user runs the risk of damaging the probe tips with each loop of the ruber band and stabbing oneself with the probe tips. Additionally, removing the probe head from the probe head mount would entail removing multiple rubber bands or multiple loops of a large rubber band with the attendant possibility of damaging the probe or the user.
A drawback to the existing probe head holders and the adaptions made by users is the rigidity of the probe heads in the probe head mounts. This is a particular drawback when using probes with closely spaced signal and ground probing tips and differential probes. The probing arm of existing probe stations is movable in the X-Y-Z directions, but may need rotational movement in the vertical plane to place the both probe tips on the device under test. This is accomplished by loosening the probe head holder at the end of the probe arm and rotating it to place the probe tips parallel to the device under test. Since very slight movement of the probing arm requires repositioning the probe head, the rotational adjustment of the probe head holder causes additional time to be expended for making measurements.
What is needed is a probe head holder for a probe arm that allows rotational movement of the probe head without having to re-adjust the position of the probe arm holder. Further, the probe head holder needs to be easily configurable with different types of probe heads.
Accordingly, the present invention is to a probe head holder usable with a probing arm of a probing station. The probe head holder has a probe head mount with a first surface adapted to receive the measurement probe head and a second surface, extending from the first surface, having at least a first groove formed therein normal to the first surface. At least a first highly elastic, high hoop strength retention member is disposed around the probe head mount and measurement probe head with a first portion disposed within the first groove in the probe head mount and a second portion disposed against the measurement probe head to flexibly secure the probe head to the mount.
In the preferred embodiment, the first surface of the probe head mount is substantially flat and the second surface is substantially round. The probe head mount has proximate and distal ends with the second surface extending over the first surface at the proximate end forming a transition extending upward from and normal to the first surface and the first and second surfaces tapering from a first dimension to a smaller second dimension at the distal end. The probe head mount is receivable in a probing arm by an attachment member disposed at the proximate end of the probe head mount. In the preferred embodiment, the attachment member has a shaft with an aperture formed therethrough that is received in a bore formed in the proximate end of the probe head mount that is parallel to the ends of the mount. Slots are formed on either side of the probe head mount that intersect the bore. A spring is disposed within the bore that engages the shaft to provide an axial spring force for the mount. A pin is disposed in the shaft aperture that engages the slots for securing the attachment member to the mount.
The highly elastic, high hoop strength retention member is preferably an elastomer ring and more specifically a castration ring used in the cattle and sheep industry. More than one groove may be formed in the second surface normal to the first surface for receiving more an one highly elastic, high hoop strength retention member. Further, the first surface of the probe head mount can have angles surfaces forming a groove that receives the probe head and the second surface may take other shapes, such as oval, rectangular, square or the like.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.